Process for reducing nitric oxide emissions from burners

ABSTRACT

This invention resides in an improved process for mixing a fuel with air and steam to form a combustible mixture and combusting said mixture in a combustion zone. In the process, the mixing of the fuel and steam is maintained in a steam to fuel ration in the range of about 0.4 to about 0.95 pound steam/pound fuel for reducing the amount of nitrogen oxides emitted during combusting of the mixture.

tlited States Patent 11 1 Alquist Nov. 26, 1974 I5 PROCESS FOR REDUCINGNITRIC OXIDE 3.238.719 3/1966 11111510111 60/DIG. 11 EMISSIONS FROMBURNERS 3,657,879 4/1972 Ewbank at 211.... 60/3905 5 l H E A B l 1] 0k]3,693,347 9/1972 Kydd et aI. OO/DIG. II 7 nventor: enr uist, art es'vie, a. A PH P C OTHER PUBLICATIONS 1 sslgnee' g bfig ompany InletManifold Water Injection for Control of Nitrogen Oxides-Theory andExperiment, J. E. Nicholls et [22] Filed: Sept. 7, 1973 al., SAETransactions, Vol. 78 Paper No. 690018 21 Appl. No.: 395,112 l PrimaryExammerW1ll1am F. ODea Related Appllcatlon Data AssistantExaminer-William C. Anderson [63] Continuation of Ser. No, 213,440, Dec.29, 1971,

abandmd; 57] ABSTRACT 52 U.S. c1 431/4, 60/DIG. 11 60/3905 Thisinventk)"resides in an improved PromS 511 1111. C1 T23 7/00 ing a fuel with airand Steam to form a combustible f Search u mixture and combusting saidmixture in a combustion 451/190 3 zone. In the process, the mixing ofthe fuel and steam is maintained in a steam to fuel ration in the rangeof [56] References Cited about 0.4 to about 0.95 pound steam/pound fuelfor reducing the amount of nitrogen oxides emitted during UNITED STATESPATENTS combusting of the mixture. 2922,408 l/I960 Humphries et al.OOIDIG. ll 3.013.383 I2/l96l Malick 60/DIG. 11 4 Clalms, 1 a ng gureINLET AIR TEMPERATURE MEASUREMENT LOCATION SPLASH COOLING RINGSCOMBUSTOR HOUSING BUSTIO AIR UST IN MIXING CYLINDER QUENCH, AIR

PIPE FLAME TUBE SECONDARY COMBUSTION AIR PRIMARY COMBUSTION AIR AIR INTO SPLASH COOLING RINGS FUEL NOZZLE SHIELD COMBUSTOR DOME FUEL IN STEAMTO COMBUSTOR PRIMARY ZONE INVENTOR. H E ALQUIST wzoo "6539200 0 minMSNNOZ 55. woz ozjoou 12 5w 0+ z m2 12 20.5528 E525. E zoiwamzou mazoumw um? M23. NEE m2 zuzmna A 7' TORNEVS PROCESS FOR REDUCING NITRICOXIDE EMISSIONS FROM BURNERS This application is a continuation ofapplication Ser. No. 213,440 filed Dec. 29. 1971, and now abandoned.

In the combustion of a mixture of fuel, air, and steam in a burner,nitrogen oxides are emitted. These nitrogen oxides are toxic and aresometimes of a sufficient concentration in the atmosphere that personsare detrimentally affected thereby.

This invention therefore resides in a process for reducing the amount ofnitrogen oxides emitted during combusting of a steam, air, and fuel bycontrolling the steam to fuel ratio of the mixture in the range of about0.4 to about 0.95.

Although the process is particularly adaptable for use with stationaryburners such as burners of an electrical power plant generating stationor other power generation facility as known in the art, said process canbe used in other burners for reducing the amount of nitrogen oxideemission therefrom.

These power plants generally combust a mixture of air, steam, and fuelsuch as heavy oil, including fuel oil containingpowdered coal or coke,residual fuels, all of which normally require some steam for properatomization. Also No. 2 heating oil and other lighter hydrocarbonsthrough liquid propane which do not'require steam for proper atomizationcan be utilized.

It has been discovered that these burners can be efficiently andeconomically operated while reducing the amount of nitrogen oxidesemitted during combustion of the fluid mixture if the ratio of the steamto fuel in the combustion zone is carefully controlled and maintained inthe range of about 0.4 to about 0.95 pound steam/pound fuel and moreparticularly in the range of about 0.5 to about 0.7 pound steam/poundfuel. At ratios less than about 0.4 the nitric oxide emissions are notreduced to a. desirable low value and at ratios greater than about 0.95the process approaches a value at which expenditures for providing thesteam are not compensated by corresponding additional nitric oxideemission reductions.

At ratios less than about 0.4 the amount of nitrogen oxides emitted isobjectionable and at ratios greater than about 0.95 the efficiency ofthe burner is less than desirable. This invention therefore sets fortha-precise combustion mixture for the combustion process which markedlyreduces the amount of nitrogen oxide pollution discharged therefromwhile maintaining the efficiency.

EXAMPLE Combustion was carried out in the combustor shown in the drawingwhich is representative of a high-heat output burner in which combustiontakes place slightly downstream from a nozzle forming a heterogeneousmixture of primary air and droplets of liquid fuel. Provision was madeto provide varying quantities of steam into the combustor primary zonethrough openings immediately surrounding the fuel nozzle. This isessentially the same point at which steam is introduced with largepowerplant steam assisted fuel spray nozzles. As a matter of conveniencethe fuel used in this experiment was a kerosene having the physicalproperties described in Table I. Although this fuel is somewhat lighterthan the heavy fuels frequently used in powerplants, it is well known tothose skilled in the art that fuel characteristics of gas or liquidfuels have only a minor influence on burner NO, emissions, i.e., NO isfixed at elevated temperatures in the primary burning gas zone of thecombustor.

The variables controlled in this experiment with this combustor aredescribed in Table II. At each of four inlet temperatures (500, 700, 900and 1,100 P) representative of various powerplant air preheat levels,and at the fuel flow and air flow conditions shown, the steam flowaround the fuel nozzle was varied between 0 and 191.2 lb/hr. Thispermitted steam/fuel ratios of from 0 to 2.48. At each condition ameasurement was made of the NO, and hydrocarbons in the exhaust from thecombustor. The method for measuring NO, was the standard Saltzman wetchemical technique. Analysis of the unburned hydrocarbons was made bythe standard flameionization technique. In order to avoid bias in theresults, the emission data were obtained in duplicate at each of the 40conditions in a statistically designed experiment.

The NO emission data from this experiment are described in Table III andthe exhaust hydrocarbon emission data are shown in Table IV. It will benoticed in comparing Tables III and IV that substantially all of the NO,emissions can be eliminated without significant increases in hydrocarbonemissions (Table IV).

There are certain other aspects of the data shown in Tables III and IVthat deserve comment. First, it is apparent that the amount of steamused to achieve proper atomization in a heavy liquid fossil .fuelpowerplant has an important benefit on NO, emissions, i.e.-, compare theNO, emissions with no steam to the NO, emissions when 02 lb.steam/lb.fuel is used. If it is desired to make a 50 percent reductionof NO emissions from present powerplants, these data suggest that such areduction can be achieved by increasing the steam/fuel ratio from thepresent level of 0.2 to approximately 0.8-0.9 lb. steam/lb. fuel (seemean values on Table III). It can be seen in Table IV that thisreduction in NO, does not compromise burner efficiency by an increase inexhaust hydrocarbons.

TABLE l-Contmued Gum, m g/ 1()0 ml 0.0

Composmon, vol 7?.

Paraffins 52.8 Physical and Chemical Prooerties of Test FuelCycloparamns Kerosene Olefins (H 80 vol 7r evaporated 442 5 xfi fi 6 590 1 Stoichiometrie Fuel/Air Ratio. lb/lb 0.0676 95 vol 7r evaporated474 End Point 496 Residue, vol 7:. 0.8 Aw 7 V 7 W l 7 HM Othermod1ficat1ons and alterat1ons of th1s 1nvent1on Gravny, dcgrccs API 46.6b h d h f Density lbs/gal M 0 w1 eeome apparent to t ose s 1 e 1n t eart rom H6111Combustion.ncLBtu/lb 1 the foregomg C11SCUSS1OI1, example,and accompanying gydmgcwcomclw drawing, and 1t should be understood thatth1s mvenmokc Pomt. mm 27.2 Sulfur. wt "/7 0.001 tlon 15 not to beunduly l1m1ted thereto.

TABLE II 2-1nch Combustor Operating Conditions Combustor Inlet Air DataCombustor and Steam Point Pressure, Air Flow, Fuel Flow, Steam Flow,Temperature Numin. Hg abs lb/sec 1b/hr 1b/hr F ber (a) Use followingschedule:

Steam Flow. Test lblhr TABLE III Effect of Steam Atomization on NitricOxide Emissions 2-1nch Combustor Inlet Steam[Fuel Ratio. lb/lb Air, F0.00 0.20 0.44 0.69 0.95 1.22 1.51 1.81 2.14 2.48

First Test With Values of Nitric Oxide in Parts ger Million on a MoleBasis Second Test 1100 338 237 208 153 111 101 55 53 39 11 1100 338 247227 175 111 98 59 49 39 16 900 234 185 173 101 44 42 26 13 900 235 174182 99 78 65 42 42 28 13 700 159 107 120 65 52 46 33 29 15 13 700 166101 110 65 49 42 39 24 16 10 500 97 71 87 71 33 36 23 16 15 0* 500 94 6872 45 36 33 23 21 16 0* Mean of Two Tests 1100 327 248 204 171 114 95669 53 38 15 900 238 174 154 69 61 42 41 23 13 700 156 107 93 78 48 3834 29 17 10 500 98 74 64 63 36 31 24 19 14 0* Mean of Two Tests WithValues of Nitric Oxide in Pounds per 1000 Pounds Fuel Flame Out.

Effect of Steam Atomization on Hydrocarbon Emissions 2-lnch CombustorInlet SteamlFuel Ratio. lb/lb Air, "F 0.00 0.20 0.44 0.69 0.95 1.22 1.511.81 2.14 2.48

First Test With Values in Terms of Parts r Million Carbon 1100 6.0 5.014.0 4.3 13.0 5.0 2.5 3.8 5.0 4.0 900 33.0 4.0 13.0 3.0 6.4 4.8 3.6 8.110.0 5.0 700 7.0 10.0 l0.0 l6.0 4.3 l 1.0 [9.3 7.5 6.8 l8.8 500 4.0 21.03.0 9.0 24.8 9.0 2.7 18.0 23.0 33.000

(Flame Out) Second Test 1100 3.0 5.0 32.0 6.0 3.9 4.7 9.0 7.0 2.7 2.5900 12.0 30.0 25.4. 4.0 4.2 6.3 7.0 3.6 3.7 2.4 700 2.0 8.0 12.7 4.0 6.63.8 6.0 9.0 7.0 7.4 500 7.0 5.0 5.1 4.0 3.7 3.3 5.7 3.0 17.0 (33,000)

' (Flame Out) Mean of Two Tests 1100 4. 5.0 23.0 5.1 8.5 4.9 5.7 5.8 3.93.3 900 22.5 17.0 19.2 6.0 5.3 5.6 6.8 5.9 6.9 3.7 700 4.5 9.0 11.3 10.05.5 7.4 12.7 8.3 6.9 13.1 500 5.5 13.0 4.1 6.5 14.3 6.l 4.2 10.5 20.0(33.000)

(Flame Out) What is claimed is: V 2. A process. as set forth in claim 1,\vl'ierein the ratio 1. In a process for mixing a fuel with air andsteam of steam to fuel of the mixture is maintained at values to form acombustible mixture and combusting said in the range of about 0.5 toabout 0.7 pound steam/- mixture in a combustion zone, the improvementcompound fuel. Pnsmg: 3. A process. asset forth in claim l 6116361111116fuel controlling the mixing of the fuel and steam for mamis oil andincluding atomizing the Steam and Oil taining the ratio of steam to fuelof said mixture in gether into the combustion Zone said combust1on zoneat values in the range of about 0.4 to about 0.95 pound steam/pound fuelfor reducing the amount of nitric oxide emitted during combustion of themixture.

a stoichiometric amount of air in injected.

' I) process, as set forth in claim '1', wherein atleast

1. IN A PROCESS FOR MIXING A FUEL WITH AIR AND STEAM TO FORM ACOMBUSTIBLE MIXTURE AND COMBUSTING SAID MIXTURE IN A COMBUSTION ZONE,THE IMPROVEMENT COMPRISING: CONTROLLING THE MIXING OF THE FUEL AND STEAMFOR MAINTAINING THE RATIO OF STEAM TO ALL OF SAID MIXTURE IN SAIDCOMBUSTION ZONE AT VALUES IN THE RANGE OF ABOUT 0.4 TO ABOUT 0.95 POUNDSTEAM/POUND FUEL FOR REDUCING THE AMOUNT OF NITRIC OXIDE EMITTED DURINGCOMBUSTION OF THE MIXTURE.
 2. A process, as set forth in claim 1,wherein the ratio of steam to fuel of the mixture is maintained atvalues in the range of about 0.5 to about 0.7 pound steam/pound fuel. 3.A process, as set forth in claim 1, wherein the fuel is oil andincluding atomizing the steam and oil together into the combustion zone.4. A process, as set forth in claim 1, wherein at least a stoichiometricamount of air in injected.